{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,14]],"date-time":"2026-03-14T12:36:43Z","timestamp":1773491803611,"version":"3.50.1"},"reference-count":15,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2014,5,27]],"date-time":"2014-05-27T00:00:00Z","timestamp":1401148800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The proposed surface water and ocean topography (SWOT) mission aims at observing short scale ocean topography with an unprecedented resolution and accuracy.  Its main proposed sensor is a radar interferometer, so a major source of topography error is the roll angle: the relative positions of SWOT\u2019s antennas must be known within a few  micrometers. Because reaching SWOT\u2019s stringent requirements with onboard roll values is challenging, we carried out simulations as a contingency strategy (i.e., to be ready if roll is larger than anticipated) that could be used with ground-based data. We revisit the empirical calibration algorithms with additional solving methods (e.g., based on orbit sub-cycle) and more sophisticated performance assessments with spectral decompositions. We also explore the link between the performance of four calibration methods and the attributes of their respective calibration zones: size and geometry (e.g., crossover diamonds), temporal variability (e.g., how many days between overlapping SWOT images). In general, the  so-called direct method (using a single SWOT image) yields better coverage and smaller calibrated roll residuals because the full extent of the swath can be used for calibration, but this method makes an extensive use of the external nadir constellation to separate roll from oceanic variability, and it is more prone to leakages from oceanic variability on roll (i.e., true topography signal is more likely to be corrupted if it is misinterpreted as roll) and inaccurate modeling of the true topography spectrum. For SWOT\u2019s baseline orbit (21 days repeat and 10.9 days sub-cycle), three other methods are found to be complementary with the direct method: swath crossovers, external nadir crossovers, and sub-cycle overlaps are shown to provide an additional calibration capability, albeit with complex latitude-varying coverage and performance. The main asset of using three or four methods concurrently is to minimize systematic leakages from oceanic variability or measurement errors, by maximizing overlap zones and by minimizing the temporal variability with one-day to three-day image differences. To that extent, SWOT\u2019s proposed \u201ccontingency orbit\u201d is an attractive risk reduction asset: the one-day sub-cycle overlaps of adjoining swaths would provide a good, continuous, and self-sufficient (no need for external nadirs) calibration scheme. The benefit is however essentially located at mid to high-latitudes and it is substantial only for wavelengths longer than 100 km.<\/jats:p>","DOI":"10.3390\/rs6064831","type":"journal-article","created":{"date-parts":[[2014,5,27]],"date-time":"2014-05-27T11:34:30Z","timestamp":1401190470000},"page":"4831-4869","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["Investigating the Performance of Four Empirical  Cross-Calibration Methods for the Proposed SWOT Mission"],"prefix":"10.3390","volume":"6","author":[{"given":"Gerald","family":"Dibarboure","sequence":"first","affiliation":[{"name":"Collecte Localisation Satellite (CLS), 8-10 Rue Hermes, 31520 Ramonville St-Agne, France"}]},{"given":"Clement","family":"Ubelmann","sequence":"additional","affiliation":[{"name":"Jet Propulsion Laboratory (JPL), 4800 Oak Grove Dr, Pasadena, CA 91109, USA"}]}],"member":"1968","published-online":{"date-parts":[[2014,5,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2325","DOI":"10.1109\/TGRS.2011.2171976","article-title":"Empirical cross-calibration of coherent SWOT errors using external references and the altimetry constellation","volume":"50","author":"Dibarboure","year":"2012","journal-title":"IEEE Trans. Geosci. Remote Sens"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"766","DOI":"10.1109\/JPROC.2010.2043031","article-title":"The surface water and ocean topography mission: Observing terrestrial surface water and oceanic submesoscale eddies","volume":"98","author":"Durand","year":"2010","journal-title":"Proc. IEEE"},{"key":"ref_3","first-page":"209","article-title":"High-Resolution Measurement of Ocean Surface Topography by Radar Interferometry for Oceanographic and Geophysical Applications","volume":"19","author":"Fu","year":"2004","journal-title":"The State of the Planet: Frontiers and Challenges in Geophysics"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"363","DOI":"10.1080\/01490419.2012.717854","article-title":"Finding desirable orbit options for the \u201cextension of life\u201d phase of jason-1","volume":"35","author":"Dibarboure","year":"2012","journal-title":"Mar. Geod"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"333","DOI":"10.1109\/5.838084","article-title":"Synthetic aperture radar interferometry","volume":"88","author":"Rosen","year":"2000","journal-title":"Proc. IEEE"},{"key":"ref_6","unstructured":"Esteban-Fernandez, D. (2013). SWOT Mission Performance and Error Budget, Jet Propulsion Laboratory. NASA\/JPL Document (Reference: JPL D-79084)."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"164","DOI":"10.3390\/s6030164","article-title":"Performances study of interferometric radar altimeters: From the instrument to the global mission definition","volume":"6","author":"Enjolras","year":"2006","journal-title":"Sensors"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1748","DOI":"10.1175\/2007JPO3773.1","article-title":"Upper ocean turbulence from high-resolution 3D simulations","volume":"38","author":"Klein","year":"2008","journal-title":"J. Phys. Oceanogr"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"214","DOI":"10.1080\/01490419.2011.584826","article-title":"Jason-2 in DUACS: First tandem results and impact on processing and products","volume":"34","author":"Dibarboure","year":"2011","journal-title":"Mar. Geod"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1276","DOI":"10.1175\/1520-0426(2003)020<1276:TAOSSS>2.0.CO;2","article-title":"The accuracies of smoothed sea surface height fields constructed from tandem altimeter datasets","volume":"20","author":"Chelton","year":"2003","journal-title":"J. Atmos. Ocean. Technol"},{"key":"ref_11","first-page":"559","article-title":"A technique for objective analysis and design of oceanographic experiment applied to MODE-73","volume":"23","author":"Bretherton","year":"1976","journal-title":"Deep-Sea Res"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"889","DOI":"10.1175\/1520-0426(2003)020<0889:CWMGFW>2.0.CO;2","article-title":"Can we merge GEOSAT follow-on with TOPEX\/POSEIDON and ERS-2 for an improved description of the ocean circulation?","volume":"20","author":"Hernandez","year":"2003","journal-title":"J. Atmos. Ocean. Technol"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"167","DOI":"10.1016\/j.pocean.2011.01.002","article-title":"Global observations of nonlinear mesoscale eddies","volume":"91","author":"Chelton","year":"2011","journal-title":"Prog. Oceanogr"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2148","DOI":"10.1002\/grl.50324","article-title":"Improvement of coastal and mesoscale observation from space: Application to the Northwestern Mediterranean Sea","volume":"40","author":"Escudier","year":"2013","journal-title":"Geophys. Res. Lett"},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Ubelmann, C., Fu, L., Brown, S., Peral, E., and Esteban-Fernandez, D. (2014). The effect of atmospheric water vapor content on the performance of future wide-swath ocean altimetry measurement. J. Atmos. Ocean. Technol, in press.","DOI":"10.1175\/JTECH-D-13-00179.1"}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/6\/6\/4831\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T21:11:53Z","timestamp":1760217113000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/6\/6\/4831"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2014,5,27]]},"references-count":15,"journal-issue":{"issue":"6","published-online":{"date-parts":[[2014,6]]}},"alternative-id":["rs6064831"],"URL":"https:\/\/doi.org\/10.3390\/rs6064831","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2014,5,27]]}}}